What Is the Ninhydrin Test for Proteins?

The ninhydrin test is a test to detect proteins. According to Dr. Ian Hunt of the Department of Chemistry at the University of Calgary, it is based on the reaction between ninhydrin and amino acids containing a free amino group to give a colored compound.

Proteins are an important part of all living cells. They are made up of amino acids. Each amino acid contains an amine group and a carboxyl group. Most amino acids and proteins are colorless. As Emeritus Professor William Reusch from Michigan State University describes, amines can react with the reagent 1,2,3-triketo-hydrindene hydrate or ninhydrin to form a blue-purple colored product. Proline reacts with ninhydrin to form a yellow-orange product. Based on this colored reaction, ninhydrin can be used to detect amino acids and proteins.

According to Dr. Hunt at the Department of Chemistry of the University of Calgary, the ninhydrin test is often used in chemistry to visualize proteins after paper or thin layer chromatography. It is also used to measure the amount of protein or amino acid quantitatively. In addition, according to the Iowa division of the International Association for Identification, the ninhydrin test is used in forensics to reveal the presence of fingerprints on surfaces.